Multilayer assembly comprising silane-grafted polyolefin

ABSTRACT

The present invention relates to a silane-grafted polyolefin, to a multilayer composition comprising said polyolefin and to an article comprising said composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European application No. EP16173727.5 filed on 9 Jun. 2016, the whole content of this applicationbeing incorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention relates to a silane-grafted polyolefin, to amultilayer composition comprising said polyolefin and to an articlecomprising said composition.

BACKGROUND ART

Transparency, adhesion, efficiency and weather resistance are mandatoryrequirements of materials for encapsulation materials of photovoltaicmodules and for several other application.

In general, photovoltaic modules that are commonly used to generatepower by conversion of light, especially sunlight, into electricity haveactive components. i.e. the components capable of converting radiationsinto electricity, that are perishable and sensitive to moisture. Forthis reason, the active components of photovoltaic modules and similardevices need to be encapsulated in sheets of materials (“encapsulant”)capable of providing protection from agents such as weather, dirt andpollution. In the most common design, the active component of the cellis protected with a sheet of glass, or of transparent plastics, on theside to be exposed to radiations (“front sheet”) and with a polymeric orcomposite layer on the opposite side (“backsheet”).

Common general practice is to use sheets of ethyl vinyl acetatecopolymer (EVA) as encapsulant of the active material. Although it iswidely used by virtue of its very low cost and common availability, EVAis affected by relevant disadvantages, mainly linked to the fact that itreleases acetic acid, which promotes corrosion of ribbons and of otherparts of the photovoltaic module. Release of acetic acid is generallyfollowed by formation of double bonds or other chromophores, inducingyellowing or browning of the film, which ultimately results in lowertransparency and diminished efficiency of the solar cells. The extent ofEVA yellowing depends on the product formulation and on the ageingconditions of the module but the colour cannot be completely avoided.Moreover, EVA generally contains high levels of radical initiators,which can lower its adhesion to the glass sheet and eventually lead todisassembly of the module.

US 2006/0201544 A (INOUE, I.) 14 Sep. 2006 describes the production ofphotovoltaic modules using filler sheets formed of copolymers ofrecurring units comprising alpha-olefins and ethylenic unsaturatedsilane compounds, wherein the filler sheets formed via extrusion arelaminated to the front/back sheets and to the other components throughacrylic resin adhesive agent layers.

WO 2012/082261 A (DOW GLOBAL TECHNOLOGIES LLC) 21 Jun. 2012 describesphotovoltaic cells, wherein films comprising alkoxysilane-containingpolyolefin resins derived from alpha-olefins with reduced melt strengthare used as encapsulants polyolefins derived from polyolefin elastomers,that are ethylene-octene copolymers, are used in the examples.

It was found that the copolymers used in the above references havesignificant drawbacks, notably they have low adherence and tend to loseit over time, similarly to the behaviour of EVA.

Thus, the need is still unmet for a material suitable to be used asencapsulant material for photovoltaic modules that overcomes thedrawbacks of EVA and of the known olefin-based materials.

SUMMARY OF INVENTION

The present invention provides a cross-linkable polymer (SPO) comprisinghydrolysable silane groups that is obtainable by polymerizing:

an olefin silane (OS) comprising hydrolysable silane groups of formulaR¹ R²R³SiY, wherein Y denotes a hydrocarbon radical comprising at leastone vinyl functional group, R¹ is a hydrolysable group and R² and R³are, independently from each other, a C₁-C₈ alkyl group or are anhydrolysable group as R¹, and

a blend (CB) of at least two copolymer (c1) and (c2) of ethylene and aC₆-C₁₀ olefin, wherein the melt flow rate (MFR) of (c1) is lower than 8g/10 min and the MFR of (c2) is higher than 10 g/10 min, as measured at190° C. and 2.16 kg.

The present invention further provides a multilayer compositioncomprising:

(a) at least one layer of glass, metal or a polymeric material (PM), and

(b) a least one polymeric layer comprising a cross-linked polyolefin(XPO) obtainable by hydrolysis and condensation of a cross-linkablepolyolefin comprising hydrolysable silane groups [cross-linkable polymer(SPO)] as defined above, wherein b) adheres directly to at least aportion of (a) and (PM) is different from (XPO) and (SPO).

The present invention also provides a process of the preparation of themultilayer composition as described above, comprising the steps of:

i. providing a layer (a) as defined above, preferably in the form of asheet;

ii. applying on at least a portion of the layer (a) of step i. acomposition comprising a cross-linkable polymer comprising hydrolysablesilane groups (SPO), and optionally suitable additives; and

iii. cross-linking (SPO) to obtain a multilayer composition, wherein thecross-linked polyolefin (XPO) adheres directly to at least a portion of(a).

The present invention further provides an article comprising themultilayer composition as defined above.

DESCRIPTION OF EMBODIMENTS

Unless otherwise specified, in the context of the present invention theamount of a component in a composition is indicated as the ratio betweenthe weight of the component and the total weight of the compositionmultiplied by 100 (also: “wt %” or “% in weight”).

In the context of the present invention, the terms “adheres” and“adhesion” indicate that two layers are permanently attached to eachother via their surfaces of contact, e.g. classified as 5B to 3B in thecross-cut test according to ASTM D3359, test method B. For the sake ofclarity, the context of the present invention does not encompassmultilayer compositions wherein a first layer and a second layer asdescribed above for layers (a) and (b) are assembled by contacting, e.g.by pressing them together without permanent adhesion between the twolayers, nor those wherein adhesion between the two layer is obtained byinterposing, also partially, a third layer of adhesive substances, suchas acrylic resins or the like.

In the context of the present invention, the term “cross-linkablepolyolefin comprising hydrolysable silane groups [cross-linkable polymer(SPO)]” is understood to mean a polymer having one or more backbonechains consisting of recurring units derived from at least onehydrogenated monomer, preferably two or more monomers, as defined aboveand one or more hydrolysable silane pendant groups.

The cross-linkable polymer (SPO) is advantageously obtained fromreaction of an olefin silane (OS) monomer comprising hydrolysable silanegroups as defined hereunder and a blend of at least two copolymers, eachcomprising recurring units derived from ethylene and from a C₆-C₈ olefinsuch as hexene, octene, or decene, preferably octene such as 1-octene,2-octene, 3-octene, 4-octene or mixtures thereof, preferably 1-octene.

By the term “hydrolysable silane groups” it is hereby intended to denotegroups of formula —Si—O—X, wherein X is a hydrogen atom or an alkylgroup, which, after hydrolysis and/or polycondensation, are capable ofcross-linking by forming —Si—O—Si— links between various polyolefinchains.

Generally, the hydrolysable silane groups have formula R¹R²R³SiY,wherein Y denotes a hydrocarbon radical comprising at least one vinylfunctional group, R¹ is a hydrolysable group and R² and R³ are,independently from each other, a C₁-C₈ alkyl group or are anhydrolysable group as R¹, wherein preferably R¹ is chosen from radicalsof the alkoxy, acyloxy, oxime, epoxy and amine type, more preferably R¹is an alkoxy radical containing from 1 to 6 carbon atoms.

By the term “vinyl functional group” it is meant a chemical groupcomprising a carbon-carbon double bond (CH₂═CH—) and derivatives formedby substitution according to the definition in the IUPAC “Compendium ofChemical Terminology, 2nd ed” (the “Gold Book”). Compiled by A. D.McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford(1997).

The term “polyolefin comprising cross-linked silane groups [cross-linkedpolymer (XPO)]” is understood to mean a polymer having one or morebackbone chains consisting of recurring units derived from at least oneunsaturated monomer, i.e. bearing at least one C═C moiety, and one ormore —Si—O—Si— links between said chains and/or one or more —Si—O— linksbetween said chains and other surfaces such as the surface of the filleror of the other layer(s).

The cross-linked polymer (XPO) is advantageously obtainable byhydrolysis and/or polycondensation from the cross-linkable polymer(SPO).

Unexpectedly, the inventors found that cross-linkable polymers (SPO)deriving from blends of at last two ethylene/C₆-C₁₀ olefin copolymers((c1) and (c2)) having different melt flow rates show improved adhesionto a substrate, as measured via compressive shear testing, with respectto the single copolymers (c1) and (c2) and to ethylene/C₄ olefincopolymers, alone or in blend with (c1) or (c2).

In the context of the present invention, the Melt Flow Rate (or MeltFlow Index, MFR) can be determined according to the methods known to theperson skilled in the art, such as, but not limiting to, ISO 1133standard procedure under a load of 2.16 Kg at 190° C.

Advantageously, in the composition of the invention the MFR of (c1) islower than 8 g/10 min, preferably lower that 6 g/10 min, more preferably5 g/10 min or lower, and that of (c2) is higher than 10 g/10 min,preferably 15 g/10 min or higher, or 30 g/10 min or higher, wherein allMFR values are measured according to ISO 1133 at 190° C. and 2.16 kg. Asa general indication, the MFR of (c1) is not lower than 0.5 or 1 g/10min and the MFR of (c2) is not higher than 80 or 70 g/10 min wherein allMFR values are measured according to ISO 1133 at 190° C. and 2.16 kg.

Preferably, in the cross-linkable polyolefin the weight ratio of(c1):(c2) in (CB) is from 80:20 to 20:80, more preferably from 75:35 to35:75, 70:30 to 30:70 or from 60:40 to 40: 60 or 50:50.

The cross-linkable polymer (SPO) typically comprises from 0.1% to 3%,preferably from 0.8% to 2.2% or 1.0% to 1.8% by weight, based on thetotal weight of the cross-linkable polymer (SPO), of hydrolysable silanegroups as defined above.

The degree of crosslinking of the cross-linked polymer (XPO) may bedetermined according to techniques known to the person skilled in theart, such as according to EN ISO 10147.

The cross-linked polymer (XPO) typically has a degree of cross-linkingof at least 40% by weight, preferably at least 50% by weight, morepreferably of at least 65% by weight.

The cross-linked polymer (XPO) typically has a degree of cross-linkingof at most 95% by weight, preferably of at most 80% by weight.

The degree of cross-linking of the cross-linked polymer (XPO) is definedas being the fraction of the cross-linked polymer (XPO) insoluble in hotxylene (extraction for eight hours at the boiling point of xyleneaccording to EN ISO 10147 standard procedure) after hydrolysis and/orcondensation of the cross-linkable polymer (SPO), that it is carried outby so-called moisture curing. Moisture curing can be made in ambientconditions (i.e. 23° C., 50% relative humidity), in hot water (from 40°C. to 95° C.). , through a vapour stream at 115° C. or in Damp HeatChamber (85° C., 85% relative humidity).

The cross-linkable polymer (SPO) according to the invention typicallyhas a melt flow index comprised between 0.1 g/10 min and 70 g/10 min,preferably in the range between 1 to 20 g/10 min, more preferably in therange between 2 to 10 g/10 min as measured, for example, according toISO 1133 standard procedure under a load of 2.16 Kg at 190° C.

The cross-linkable polymer (SPO) according to the invention preferablyhas a standard density comprised between 850 kg/m³ and 960 kg/m³,preferably between 860 kg/m³ and 900 kg/m³, more preferably between 870kg/m³ and 890 kg/m³, more preferably between 870 kg/m³ and 880 kg/m³.

In the context of the present invention, as a non-limiting example, thestandard density can be measured according to ASTM D792-08 standardprocedure (method B, absolute ethanol).

The cross-linkable polymer (SPO) is typically obtainable by processingtwo or more polyolefins ((c1) and (c2)) in the presence of a compoundcomprising hydrolysable silane groups. (SPO) can contain further ahomopolymer or a copolymers obtained from polymerization of one or moreC₂-C₈ alkenes (component (c3)).

Said polyolefin (c3) is preferably a polyethylene such as an ethylenehomopolymer or a copolymer of ethylene with another monomer selectedfrom C₃-C₈ alkenes. Alternatively, the polyolefin (c3) is preferably apolypropylene such as an propylene homopolymer or a copolymer ofpropylene with another monomer selected from C₃-C₈ alkenes.

The polyolefin (c1), (c2) and, optionally, (c3) in the polymer (SPO) ofthe present invention is more preferably at least one or more blend ofpolyethylene made with different catalytic system as Ziegler-Natta,chromium, metallocene and non metallocene. Said polyolefin is morepreferably at least one or more blend of polyethylene selected from agroup of a low density polyethylene, a medium density polyethylene, ahigh density polyethylene, ultra high density polyethylene, a very lowdensity polyethylene, ultra low density polyethylene and linear lowdensity polyethylene according to the definition generally known to theperson skilled in the art, e.g. according to the classification reportedin ASTM D883-12 and in Ullmann's Encyclopedia of Industrial Chemistry6th Edition, 2000, “Polyolefins”.

The polyolefin (c1), (c2) and, optionally, (c3) in the polymer (SPO) ofthe present invention is preferably a polyethylene copolymer such ascopolymer of ethylene with another monomer selected from C₆-C₁₀ alkenes,preferably from C₆-C₈ alkenes, preferably C₈ alkenes. The cross-linkablepolymer (SPO) is generally manufactured by melt processing the blend oftwo or more polyolefins in the presence of a compound comprisinghydrolysable silane groups and of a compound capable of generating freeradicals.

Non-limitative examples of compounds comprising hydrolysable silanegroups suitable for use in the manufacture of the cross-linkable polymer(SPO) include copolymers including recurring units bearing vinylsilanes.

The cross-linkable polymer (SPO) is generally manufactured by meltprocessing one or more polyolefins as indicated above in the presence offrom 0.5% to 3.5% by weight, based on the total weight of thepolyolefin(s), of a vinyl silane and from 0.01% to 0.5% by weight, basedon the total weight of the polyolefin(s), of a compound capable ofgenerating free radicals.

Very good results have been obtained with ultra low densitypolyethylene. It is preferable to use a blend of resins of ultra lowdensity polyethylene, that is a blend of resins of copolymer of ethylenewith another monomer selected from C₆-C₁₀ alkenes, preferably from C₆-C₈alkenes, preferably C₈ alkenes.

The polyethylene used in the process for manufacturing thecross-linkable polymer (SPO) has a standard density comprised between860 kg/m³ and 960 kg/m³, preferably between 860 kg/m³ and 880 kg/m³,more preferably between 865 kg/m³ and 875 kg/m³.

The polyethylene(s) has (have) a melt flow index comprised between 0.1g/10 min and 70 g/10 min, more preferably between 3 g/10 min and 40 g/10min, as measured according to ISO 1133 standard procedure under a loadof 2.16 Kg at 190° C.

The polyethylene(s) has (have) a melting temperature comprised between30° C. and 140° C., preferably between 40° C. and 70° C., wherein themelting temperature is measured according to ISO 306.

By the term “compound capable of generating free radical” it is herebyintended, for example, peroxides and azo compounds, or by ionizingradiation, etc. A suitable azo- compound is azobisisobutyl nitrile(AlBN).

As non-limiting examples, suitable radical initiators are those reportedin WO 2012/082261 A (DOW GLOBAL TECHNOLOGIES, LLC) Jun. 21, 2012 Organicfree radical are preferred, such as any one of the peroxide initiators,for example, dicumyl peroxide, di-tert-butyl peroxide, t-butylperbenzoate, benzoyl peroxide, cumene hydroperoxide, t-butyl peroctoate,methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexane, lauryl peroxide and tert butyl peracetate.

By the term “vinyl silane” it is hereby intended to denote a silanecomprising at least one vinyl functional group. The vinyl silane used inthe process for manufacturing the composition (C) is usually a vinylsilane of formula R¹R²R³SiY, wherein Y denotes a hydrocarbon radicalcomprising at least one vinyl functional group, R¹ denotes ahydrolysable group and R ² and R³ denote, independently, an alkyl groupor a hydrolysable group R¹. The hydrolysable group R¹ may be chosen fromradicals of the alkoxy, acyloxy, oxime, epoxy and amine type. R¹ ispreferably an alkoxy radical containing from 1 to 6 carbon atoms.

It is preferred to use a vinyl silane of formula R¹R²R³SiY, wherein R²and R3 are also hydrolysable groups R1 as defined above.

Good results have been obtained with vinyltrialkoxysilanes wherein R¹,R² and R³ are alkoxy groups containing from 1 to 4 carbon atoms.Particularly preferred are vinyltriethoxysilane andvinyltrimethoxysilane.

The amount of vinyl silane used in the process for manufacturing (SPO)is preferably comprised between 1.3% and 2.6% preferably from 1.5 to 2.0or from 1.6 to 1.8% by weight, based on the total weight of thepolyolefin(s).

Composite material (C) can be mixed (via addition, suitably duringcompounding or extrusion/injection) with a specific catalyticmasterbatch (CM) containing, but not limited to, anti-oxidants and/or UVabsorbers and/or flame retardants and/or anti-dripping agents and/orpigments and reflective materials and/or silanol condensation catalystand/or down/up converter. As used herein, the term “down/up converter”indicates one or more organic/inorganic molecule(s) or complex orsalt(s) or blend of them, that is able to absorb of one or more photonsand leads to the emission of light at shorter or higher wavelength thanthe excitation wavelength. A non-limiting example is the conversion ofinfrared light to visible light. Materials by which down/up conversioncan take place often contain ions of d-block and f-block elements.Non-limiting examples of these ions are Ln³⁺, Ti²⁺, Ni²⁺, Mo³⁺, Re⁴⁺,Os⁴⁺, and the like.

As non-limiting example, suitable anti-oxidants can be chosen from awide range of known anti-oxidants that are compatible with polyolefins.Examples include but are not limited to phenolic or phosphiticanti-oxidants, such as alkylated monophenols, alkylthiomethylphenols,hydroquinones, alkylated hydroquinones, tocopherols, hydroxylatedthiodiphenyl ethers, alkylidenebisphenols, acylaminophenols. Otherexamples include but are not limited to O-, N- and S-benzyl compounds,hydroxybenzylated malonates, aromatic hydroxybenzyl compounds, triazinecompounds, aminic antioxidants, aryl amines, diaryl amines, polyarylamines, oxamides, metal deactivators, phosphites, phosphonites,benzylphosphonates, ascorbic acid (vitamin C), compounds which destroyperoxide, hydroxylamines, nitrones, benzofuranones, indolinones, and thelike and mixtures thereof. More preferably, the antioxidant is a memberof the class of bis-phenolic antioxidants. Suitable specificbis-phenolic antioxidants include2,2′-ethylidenebis(4,6-di-t-butylphenol);4,4′-butylidenebis(2-t-butyl-5-methylphenol);2,2′-isobutylidenebis(6-t-butyl-4-methylphenol); and2,2′-methylenebis(6-t-butyl-4-methylphenol). Some commercially availablebis-phenolic antioxidants include ANOX® 29, LOWINOX® 22M46, LOWINOX®44625, and LOWINOX® 221 B46.

Typical examples of UV absorbers include but are not limited totriazines, benzotriazoles, hydroxybenzophenones, hydroxyphenyltriazines,esters of benzoic acids, and mixtures of two or more thereof. Furtherexamples include cyclic amines. Examples include secondary, tertiary,acetylated, N-hydrocarbyloxy substituted, hydroxy substitutedN-hydrocarbyloxy substituted, or other substituted cyclic amines whichare further characterized by a degree of steric hindrance, generally asa result of substitution of an aliphatic group or groups on the carbonatoms adjacent to the amine function.

Examples of flame retardants include but are not limited to halogenatedaromatic compounds, like halogenated biphenyls or biphenyl ethers andbisphenols. Typically the halogenated materials are brominated orpolybrominated. Specific examples include bisphenols like polybrominatedbiphenyl, penta-, octa- and deca-brominated diphenyl ethers (BDE's),tetrabromobisphenol-A (TBBPA). Further examples include but are notlimited to inorganic compounds like alumina trihydrate, antimony oxide,magnesium hydroxide, zinc borate, organic and inorganic phosphates, redphosphor and combinations thereof.

Typically, anti-dripping agents include, but are not limited to,fluoropolymers, such as a polytetrafluoroethylene polymers andcopolymers. The anti-dripping agents may be dispersed in or blended withthe polymer making up the respective layer. Commercial examples ofanti-dripping agents include MM5935EF from Dyneon® LLC, ALGOFLON® DF210from Solvay Specialty Polymers or ENTROPY® TN3500 from Shanghai EntropyChemical.

Pigments may be inorganic or organic. Pigments may be of green, blue,red, pink, purple and white colour. Most commonly used white pigmentsare inorganic pigments. Examples include but are not limited to zincoxides and titanium oxides (like TiO₂) or carbon particles. The pigmentsmay be dispersed, blended or dissolved in the layer but may be paintedor printed onto a layer.

Reflective materials include glass particles or metal particles, withglass particles being preferred. They may be dispersed, blended ordissolved in a layer.

A catalytic masterbatch can be added in an amount from 0.5 to 10% byweight, more preferably from 2 to 5% by weight, based on the totalweight of the polyolefin(s); the amount is strongly depending theperformances required to specific end use, as known to the personskilled in the art.

By the term “silanol condensation catalyst” it is hereby intended thesystem able to accelerate the reaction of hydrolysis and/or condensationthe cross-linkable polymer (SPO) that it is carried out by so-calledmoisture curing, such as in WO 91/07075 A (NESTE OY) Jun. 27, 1991.Prior art silanol condensation catalyst include carboxylates of metals,such as tin, zinc, iron, lead and cobalt, organic bases, inorganicacids, and organic acids. Special mention should be made of dibutyl tindilaurate, dibutyl tin diacetate, dioctyl tin dilaurate, stannousacetate, stannous caprylate, zinc caprylate, ethyl amines, dibutylamine, hexylamines. Inorganic acids such as sulphuric acid as well asorganic acids such as toluene sulphonic acid, stearic acid and maleicacid can also be uses. Preferably the silanol condensation catalyst is ametal carboxylate, more preferably a tin carboxylate.

The compositions of the present invention have similar, or improvedstarting performances with respect to the known compositions in terms ofadhesion, efficiency, transparency and weather resistance in multilayerassembly. The adhesion of the compositions of the present invention tothe substrates improves over time, whereas conventional materials suchas EVA tend to lose adhesion to the substrates over time.

Layer (a) is preferably formed of glass, such as high transparencyglass, metal (such as aluminium, titanium their alloys or steel) or of(PM) that is selected from the group consisting of polycarbonates,acrylic polymers, polyacrylates, cyclic polyolefins such as ethylenenorbornene, metallocene-catalyzed polystyrene, polyethyleneterephthalate (PET), polyethylene terephthalate bioriented (BOPET),polyethylene naphthalate, fluoropolymers such as ETFE(ethylene-tetrafluoroethylene), PVF (polyvinyl fluoride), FEP(fluoroethylene propylene), ECTFE (ethylene chlorotrifluoroethylene),PVDF (polyvinylidene fluoride), and laminates, mixtures or alloys of twoor more thereof.

Layer (a) is preferably formed of PET, ECTFE or glass, more preferablyit comprises, or consists of, glass.

When used in certain embodiments of the present invention, “glass”refers to a hard, brittle, transparent solid, such as that used forwindows, many bottles, or eyewear, including, but not limited to,soda-lime glass, borosilicate glass, acrylic glass, sugar glass,phyllosilicates such as mica (isinglass or Muscovy-glass), or aluminumoxynitride. In the technical sense, glass is an inorganic product offusion which has been cooled to a rigid condition without crystallizing.Many glasses contain silica as their main and glass-former component.

Pure silicon dioxide (SiO₂) glass (the same chemical compound as quartz,or, in its polycrystalline form, sand) does not absorb UV light and isused for applications that require transparency in this region. Largenatural single crystals of quartz are pure silicon dioxide, and uponcrushing are used for high quality specialty glasses. Syntheticamorphous silica, an almost 100% pure form of quartz, is the rawmaterial for the most expensive specialty glasses.

The glass layer of the multilayer composition according to the inventionis typically one of, without limitation, window glass, plate glass,silicate glass, sheet glass, float glass, colored glass, specialty glasswhich may, for example, include ingredients to control solar heating,glass coated with sputtered metals such as silver, glass coated withantimony tin oxide and/or indium tin oxide, E-glass and similarmaterials.

The multilayer composition can be uses for different applications as,but not limited to, healthcare, plumbing, safety glass and safety glasswindows, packaging, one or more electronic devices included, but notlimited to, solar cells rigid or flexible modulus (also known asphotovoltaic cells), liquid crystal panels, electro-luminescent devicesand plasma display units, DSSC (Day Sensitize Solar Cells).

XPO can be used as encapsulant, for example in a photovoltaic cell, orsealant in shape of film or strip layer and it need to adhere with otherlayers in laminated or co-extrude multilayer assembly.

In an embodiment of the present invention, the (XPO) is used asencapsulant layer in photovoltaic (PV) cell or modulus. In such devices,the encapsulant need not only to adhere at different substrates but alsoto protect cells from moisture and other types of physical damage, toguarantee optical clarity and physical retention properties at hightemperature and all requirements indicated in IEC 61215 standard for PVcells. The encapsulants as described above that are based on (SPO) canbe used in various PV technologies as, but not limited to, crystallinesilicon, polycrystalline silicon, amorphous silicone, copper indiumgallium (di)selenide (GIGS), copper indium selenide (CIS), cadmiumtelluride, gallium arsenide, CdTE, OPV, dye-sensitized materials andperovskite.

The typical polymeric encapsulant materials generally used for thesepurposes include silicon resins, epoxy resins, polyvinyl butyral resins(PVB), cellulose acetate, ethylene-vinyl acetate copolymer (EVA),ethylene-vinyl acetate copolymer cross-linked by peroxide method (EVAcross-linked), ionomers and thermoplastic polyolefins.

In another aspect, the present invention provides a process for theproduction of the film for encapsulant application as defined above,comprising the steps of:

(I) providing a polyolefin comprising cross-linkable silanol group (SPO)as defined above, which, optionally, can be physically blended withcatalytic masterbatch (CM) as defined above;

(II) extruding (SPO), which optionally includes (CM), in the form of afilm;

(III) optionally, partial cross-linking of the (SPO) silanol groups.

Optionally, cross-linking of the silanol groups of (SPO) is completedafter assembly of the multilayer structure. The polyolefin comprisingcross-linkable silanol groups (SPO) can be prepared in form of pellet,powder flakes or powder, preferably in pellet form. Any conventionalmethod can be used, reactive extrusion being preferred. The most commonreactive extrusion methods useful for the preparation of (SPO) are namedMonosil™ (one step) and Sioplas™ (two-step) reactive process.

The one-step Monosil™ process was developed by Maillefer as aone-step-process where all of the components of the polyolefin baseresin, additives, peroxide and silane are grafted in a specializedcompounding extruder which also extrudes the film in-line.

The two-step Sioplas™ process was invented and patented by Dow

Corning. This process requires extruding (SPO) from a reactive compoundcomposed of silane groups which have been grafted onto polyolefin (PO)polymer chains by the addition of organic peroxide in an offlinecompounding process.

One preferred method is blending cross-linkable polymer (PO), vinylsilane and free radical generator, in any conventional reactor extruder,such as, but not limited to, a Buss kneader or mono or twin screw,preferably a twin screw extruder. The conditions can vary depending uponthe residence time and the half-life of the free radical generator butthe temperatures profile is typically in the range from 110 to 190° C.,depending mostly from the melting temperature of the PO.

In an aspect, the present invention is relative to a process for thepreparation of the multilayer composition as defined above, comprisingthe steps of:

i. providing a layer (a) as defined above comprising glass, metal or apolymeric material (PM) different from (XPO), preferably in the form ofa sheet;

ii. applying on at least a portion of the (a) layer of step i. acomposition comprising a cross-linkable polymer comprising hydrolysablesilane groups (SPO) as defined above, and optionally suitable additives;

iii. cross-linking the (SPO) to obtain a multilayer composition, whereinthe cross-linked polyolefin (XPO) adheres directly to at least oneportion of (a).

The cross-linkable polymer comprising hydrolysable silane groups (SPO)can optionally be partially cross-linked prior to its application to thelayer (a) in step ii. The partial cross-linking of the (SPO) can becarried out during its preparation, e.g. during extrusion of the layerin the form of a film, or after its preparation in the form of a sheetor film. Typically, after that step, the cross-linking degree is in therange from 0% to 30%, preferably from 0% to 10%, preferably from 0% to5%. The step of partial cross-linking needs to be evaluated forobtaining the good balance between the properties of the portion notcross-linked, that is necessary to allow the multilayer assemblyprocess, and those of the cross-linked portion, that is necessary toensure the final performance required, expecially in term of creep athigh temperature.

In the step iii. of the process according to the invention the layer (b)of the multilayer composition can be partially or totally cross-linked.

Optionally, in the step iii. of the process according to the inventionthe multilayer composition can be totally cross-linked to achieve thehigher performances, especially in terms of adhesion, thermalresistance, creep at temperature above the melting temperature of SPO.The maximum cross-linking degree of step (iii), typically, is in therange from 50% to 90%, preferably from 60% to 80%. It was found that bycross-linking the multilayer assembly for more than 500 hours in a dampheat chamber (85° C.; 85% relative humidity) the adhesion, withdifferent layers, increases.

The partial or total cross-linking of the (SPO) silanol groups can becarried out by any curing method using moisture, which accelerates thecross-linking process.

It is possible, but not necessary, to add a catalytic masterbatch, thatcan be mixed together with (SPO) in a step (ii). The catalyticmasterbatch promotes a faster cross-linking in the multilayer assemblyand allows to achieve an higher performance, especially in terms ofresistance to creep at temperature above the melting temperature of SPO.

As non-limiting examples, the film can be formed by any of theconventional extrusion method such as casting, doctor blade, lamination,spin coating, dip coating, co-extrusion, by hydraulic pressure, filmextrusion, cast extrusion, preferably by film extrusion. The typicaltemperatures profile is in the range from 120° C. to 180° C., dependingmostly from the melting temperature of the (SPO) being used.

In an aspect, the present invention provides an article comprising themultilayer composition as described above.

In an aspect the present invention provides a photovoltaic (PV) cell,which comprises at least the following layers: a “frontsheet” layer(FS), a first encapsulant layer, a solar cell, a second encapsulantlayer and a “backsheet” (BS) layer, wherein at least the “frontsheet”layer (FS) and the first encapsulant layer are formed of the multilayercomposition comprising layers (a) and (b) as defined above.

In the context of the invention, by “frontsheet” layer (FS) it isintended to denote the outer layer of a PV cell which is exposed to theenvironment and to incident electromagnetic radiation. The FS of the PVcell of the invention is described above as layer (a).The thickness ofFS layer is not particularly limiting, preferably it is 6 mm or below.The optically transparent layer FS advantageously has a transmittance ofat least 70%, preferably of at least 80%, more preferably of at least85% of the incident electromagnetic radiation, as measured according toASTM D1003 standard procedure under atmospheric air.

The first encapsulant layer in the PV cell of the invention is describedabove as layer (b). The thickness of the first encapsulant layer in thePV cell is not critical and it may depend on the use for which saidassembly is intended. In general, for PV cells the preferable thicknessis in the range from 200 microns to 600 microns.

For the solar cell, i.e. the active component, in the PV cell of theinvention different PV technologies can be used as described above.

The second encapsulant layer in the PV cell of the invention can bepreferably composed of the (XPO) polymer as described above or it can becomposed of a polymer different from (XPO).

The thickness of the second encapsulant layer in the PV cells is notcritical and will depend on the use for which said assembly is intended.For PV cells according to the invention, its preferable thickness is inthe range from 200 microns to 600 microns.

In the PV cell according to the invention, a “backsheet” (BS) layer ispresent that is the outermost layer of the PV module and is designed toprotect the inner components of the module, specifically thephotovoltaic cells and electrical components from external stresses aswell as act as an electric insulator. The thickness of the BS layer isnot particularly limited as it depends on the type of material used,preferably it is less than 6 mm.

Each of the FS and BS layers can be made by one or more of the knownrigid or flexible sheet materials, included for example, glass, hightransparency glass, polycarbonate, acrylic polymers, polyacrylate, acyclic polyolefin such as ethylene norbornene, metallocene-catalyzedpolystyrene, polyethylene terephthalate (PET), polyethyleneterephthalate bioriented (BOPET), polyethylene naphthalate,fluoropolymers such as ETFE (ethylene-tetrafluoroethylene), PVF(polyvinyl fluoride), FEP (fluoroethylene propylene), ECTFE (ethylenechlorotrifluoroethylene), PVDF (polyvinylidene fluoride) and many othertypes of plastic, polymeric or metal materials, included laminatesmixtures or alloys of two or more these materials as known to the personskilled in the art (ref. patent WO 2012/082261 A (DOW GLOBALTECHNOLOGIES LLC) 21 Jun. 2012 par. [0054])

In general, the multilayer assembly can be made in a different ways as,but not limited to, compression in temperature, lamination process. Forassembling the system typically the temperature, time and otherparameters are set to ensure the sufficient adhesion between the layers.

In another aspect the present invention provides also an articlesuitable for use in glass safety and glass safety windows, whichcomprises at least the following layers: a “frontsheet” layer (FS); asdescribe in multilayer assembly for PV cells, an encapsulant layer; asdescribe in multilayer assembly for PV cells and a “backsheet” (BS)layer; as describe in multilayer assembly for PV cells.

The compositions according to the following examples have shown superiorperformances over time (aging in Damp Heat standard conditions, i.e. 85°C. and 85% relative humidity) as encapsulants in terms of adhesion(Peeling test), durability (mini-modulus efficiency) and weatherresistance in multilayer assembly (in the specific case for PV cells) inapplications where maintaining good transparency (Total Transmittance,Haze, Yellow Index, Withe Index, UV-Vis, NIR) over time is a must. Someresults have been compared, using the same samples preparation, withcross-linked EVA as first and second encapsulants, that is widely usedas encapsulant for PV cells.

Should the disclosure of any patents, patent applications, andpublications which are incorporated herein by reference conflict withthe description of the present application to the extent that it mayrender a term unclear, the present description shall take precedence.

The following examples are provided to illustrate the invention, withoutintention to limit its scope.

Experimental Part

Four different types of polyolefine encapsulants with silane graftingwere prepared by mixing one or two polyolefin(s) with a vinylsilane. Onecomparative EVA-containing encapsulant was also prepared.

The SPO film was prepared in the following steps:

Step a): a polyolefin comprising cross-linkable silanol group (SPO) wasprepared in form of pellets via Sioplast™ reactive process withextrusion in a twin screw extruder, the temperatures profile is in therange from 120 to 160° C.

Step b): In this example, the SPO has not been blended with catalyticmasterbatch (CM)

Step c): the SPO was extruded in form of film (200 or 400 or 600 micronof thickness), the temperatures profile was in the range from 130 to160° C.

The polyolefin comprising cross-linkable silanol groups (SPO) can beprepared in form of pellets, flakes or powder, preferably in pelletform. Any conventional method can be used, the common are named Monosil™(one step) and Sioplas™ (two-step) reactive process; one preferredmethod is blending cross-linkable polymer (PO), vinyl silane and freeradical generator, in any conventional reactor extruder, such as, butnot limited to, a Buss kneader or mono or twin screw, preferably a twinscrew extruder. The conditions can vary depending upon the residencetime and the half-life of the free radical generator but thetemperatures profile is typically in the range from 110 to 190° C.,depending mostly from the melting temperature of the PO.

Table 1 shows the polyolefins/blend of polyolefins used in the examples(% amounts are in weight of the component based on the total weight ofthe components (c1) and(or (c2)) . In all comparative examples 1-3 andinventive examples 4, 4a (same composition as 4) and 5, the amount ofvinyl silane is from 1.4 to 1.8% by weight based on the total weight ofthe polyolefin(s).

TABLE 1 Polyolefin A CO 1 B C CO 2 MFR 190° 5 5 30 15 35 C. 2.16 kgMonomers Ethylene/ Ethylene/ Ethylene/ Ethylene/ Ethylene/ compositionoctene butene octene octene butene Comp Ex 1 100%  — — — — Comp Ex 2 70%— — — 30% Comp Ex 3 — 100% — — — Ex 4/4a 70% — 30% — — Ex 5 70% — — 30%—

The EVA used as comparative material in the experiment is a 0.45 mmthick EVASKY® S88 from Bridgestone.

Adherence to Glass

In order to compare the encapsulants at similar thicknesses, in themechanical and optical testing two layers of polyolefine having the samethickness and only one layer of EVA were used in the sample preparation.The encapsulants were extruded to the thickness indicated below and 30cm width.

Two layers of each of the different encapsulants were laminated in avacuum laminator between two glass plates (100×100×3.0 mm, Eurowhitequality) with a standard cycle used for EVA (150° C., 300 s pumping, 600s curing). Prior to encapsulation the glasses were cleaned withisopropanol. The laminated samples were then cut with an automateddiamond saw down to 25×25 mm samples and tested in a Compressive ShearTesting (CST) set up. Part of the samples were aged in Damp Heat (DH)conditions (85° C., 85% relative humidity, RH) for 300 h and thentested.

Each reported value is the average of 5 measurements. To avoid possibleinconsistencies in the mechanical properties of the encapsulants, forall the samples the direction of the applied shear stress correspondedto the extrusion direction.

The results of CST testing are expressed in terms of “stored elasticenergy” needed to start delamination of the samples during the appliedshear stress. The higher this value the more resistant to delaminationwill be the encapsulant/glass interface.

Results

The laminated 10×10 cm glass/glass samples did not show visually anybubble or delamination after lamination.

The Compressive Shear Testing results are summarized in Tables 2 and 3and show different behaviours for the different encapsulants.

In Table 2 are shown the values of Compressive Shear Testing carried outusing two layers of polyolefine (2×0.35 mm) and only one layer of EVA(0.8 mm) were used in the sample preparation.

TABLE 2 Stored elastic energy Sample (mJ/mm3) Comp Ex. 1 3 Comp Ex. 2 4Ex. 4 11 Ex. 5 8 Comp Ex EVA 27

The compositions of examples 4 and 5, according to the invention, whichcomprise a blend of an ethylene/octene polyolefin having high MFR withan ethylene/octene polyolefin having low MFR, have notably higherresistance to delamination with respect to the comparative compositionswhich comprise only a ethylene/octene polyolefin having low MFR (Comp.Ex. 1, containing polyolefin A) or a mixture of the same ethylene/octenepolyolefin with a ethylene/butene polyolefin (CO 2) having high MFR(Comp. Ex. 2).

The Compressive Shear Testing results obtained for samples before andafter aging for 300 hours in Damp Heat conditions are summarized inTable 3 and show a different behaviour for the different encapsulants.In order to compare the encapsulants at similar thicknesses, two layersof polyolefine having the same thickness (2×0.2 mm) for comparativeexample 3 and example 4a according to the invention and only one layerof EVA (0.45 mm, comparative example 3a) were used in the samplepreparation.

TABLE 3 Stored elastic energy (mJ/mm3) After 300 hours aging in SampleInitial values DH (85° C., 85% RH) Comp Ex. 3 7.5 5 Ex. 4a 25 39 CompEVA 39 19

All the observed delaminations were of adhesive nature, i.e. they werelocated at the glass/encapsulant interface and not within theencapsulant itself.

The values of this series of measurements are higher than the values ofthe series of samples of Table 2. This difference can be empiricallyexplained by higher thickness of the encapsulate of the first seriescompared to the second series (from about 0.7 mm to about 0.4 mm forpolyolefins and from about 0.8 mm to about 0.45 mm for EVA). Due tonon-linearity in the thickness-shear force behaviour the overall energyneeded for sample failure tend to decrease with increasing encapsulantthickness.

The formulation of Comparative Example 3a shows the lowest values beforeand after aging.

The formulation of Example 4 shows an high initial value and aremarkable increase over time. On the contrary, in comparative example6, wherein EVA is used as the encapsulant, the adhesion after 300 hoursof aging under Damp Heat conditions decreases to about half of theinitial value.

Optical Properties

One layers of each of the different encapsulants was laminated in avacuum laminator between two glass plates (5×5×3.2 cm, from F-Solar,Solarfloat type T quality) with a standard cycle used for EVA (155° C.,300 s pumping, 900 s curing). After lamination the samples were cooledin air.

The samples were then measured with a Perkin Elmer UV-VIS instrument ina 320-2000 nm wavelength range. Both total transmission (TT) and diffusetransmission (DT) curves were acquired and the Haze (defined as theDT/TT ratio) was then calculated at 400 nm.

The results can be evaluated in terms of percentage of transmitted light(total or diffuse). The higher the TT the higher will be the lightreaching the solar cell. Concerning the diffuse light, the lower is theHaze value and the lower will be the milky appearance of the PV moduleand the batter its aesthetically acceptance.

All tested compositions have a DT/TT ratio at 400 nm (the so called“Haze factor”) ranging between 5-8%, that is an acceptable value for theintended applications in the photovoltaic area. From the practical pointof view it is commonly observed that only starting from Haze factorshigher that 10-15% a milky appearance can be appreciated by bare eye andthe value measured for the samples according to the invention aretherefore not relevant to impact the aesthetical acceptance.

The above data demonstrate that the compositions according to theinvention have higher resistance to peeling that those comprisingpolyolefins different from (c1 and (c2) as defined above. In addition,the high resistance to peeling of the compositions according to theinvention increases upon aging in Damp Heat conditions, whereas that ofconventional encapsulants comprising EVA rapidly decreases tounacceptable levels under the same conditions.

In addition, all compositions according to the present invention showedacceptable transparency in optical property tests (haze lower than 9%),that is suitable for application in photovoltaic cells and similardevices.

PV Cell Efficiency

To evaluate efficiency of a photovoltaic cell comprising the multilayermaterial according to the invention, the mini-modulus PV cell (20 cm*20cm) was prepared by lamination process (150° C., 300 s pumping, 900 scuring) and comprises the following layers:

A “frontsheet” layer (FS) with high transparency glass for PV-grade, lowiron, 3.0 mm thickness;

A first encapsulant layer;

A solar cell made with poly-Silicon solar;

A second encapsulant layer;

A “backsheet” layer (BS) with high transparency glass for PV-grade, lowiron, 3.0 mm thickness.

In the cell according to the invention, the cross-linkable polymer (XPO)(film, 400 micron of thickness) as defined above was used as first andsecond encapsulant layers, and in a comparative example a PV cell wasprepared using EVA (commercially available film, 450 micron ofthickness).

PV cell efficiency was measured at 25° C. with a solar simulator,according to IEC EN 61215 10.13. For sake of clarity, figures regardingPV efficiency and other performances are normalized (100% at t=0 foreach value and each module) in Table 4 are reported the values obtained.Aging tests was carried out in Damp Heat chamber (DH) at 85% humidity,85° C. for different times (500, 1000, 2000, 3000 hours), according toIEC EN 61215.

TABLE 4 Table 4: Mini-modulus efficiency of PV cell according to theinvention. 500 h 1000 h 2000 h 3000 h Encapsulant DH DH DH DH XPO Isc(%) 100 100 100 100 Fill Factor (%) 99 99 98 98 Normalized 98 100 97 96Efficiency (%)

Cells comprising the multilayer compositions according to the inventionas FS and BS maintained excellent efficiency of operation over time,with a slight improvement with respect to the initial values after 1000h in DH.

In comparative examples, during aging in DH, it was observed thatcross-linked EVA (laminated with high transparency glass as FS and BS)loses the efficiency after 1000 hours and it does not reach the limitsrequired, according to IEC 61215 for PV application.

Example 4. Mini-modulus PV cell (20 cm*20cm) laminated with Halar®

UV blocking as FS and BS. Comparison between SPO grade and cross-linkedEVA.

TABLE 5 Table 5: Mini-modulus PV cell efficiency 1000 h 2000 hEncapsulant DH DH SPO Isc (%) 100.05 98.74 Fill Factor (%) 93.33 95.55Normalized 93.70 93.46 Efficiency (%)

TABLE 5-a Table 5-a: Mini-modulus PV cell efficiency; comparativeexample 1000 h 2000 h Encapsulant DH DH EVA Isc (%) 96.35 61.72 FillFactor (%) 92.46 50.14 Normalized 88.72 28.18 Efficiency (%)

As shown in Tables 5-5a, during aging in DH conditions, cross-linked EVA(laminated with Halar UV blocking as FS and BS) loses the efficiencyafter 1000 hours and after 2000 hours it does not achieve the limitrequired according to IEC 61215 for PV application. The modulecomprising the composition according to the invention maintains verygood efficiency also after 3000 hours.

1. A cross-linkable polymer (SPO) comprising hydrolysable silane groupsthat is obtainable from reaction of: an olefin silane (OS) comprisinghydrolysable silane groups of formula R¹R²R³SiY, wherein Y denotes ahydrocarbon radical comprising at least one vinyl functional group, R¹is a hydrolysable group and R² and R³ are, independently from eachother, a C₁-C₈ alkyl group or are an hydrolysable group as R2 ¹, and ablend (CB) of at least two copolymer (c1) and (c2) of ethylene and aC₆-C₁₀ olefin, wherein the melt flow rate (MFR) of (c1) is lower than 8g/10 min and the MFR of (c2) is higher than 10 g/10 min, as measured at190° C. and 2.16 kg.
 2. The cross-linkable polyolefin of claim 1,wherein (OS) is a vinyl silane and/or R¹ is chosen from radicals of thealkoxy, acyloxy, oxime, epoxy and amine type, more preferably R¹ is analkoxy radical containing from 1 to 6 carbon atoms.
 3. Thecross-linkable polyolefin of claim 1, wherein the weight ratio of(c1):(c2) in (CB) is from 80:20 to 20:80.
 4. A multilayer compositioncomprising: (a) at least one layer of glass, of a metal or of apolymeric material (PM), and (b) a least one polymeric layer comprisinga cross-linked polyolefin (XPO) obtainable by hydrolysis andcondensation of a cross-linkable polyolefin comprising hydrolysablesilane groups [cross-linkable polymer (SPO)] according to claim 1,wherein b) adheres directly to at least a portion of (a) and (PM) isdifferent from (XPO).
 5. The multilayer composition according to claim4, wherein (XPO) is obtainable via hydrolysis and condensation of thecross-linkable polyolefin (SPO) comprising from 0.1% to 3% in weightbased on the total weight of (SPO) of hydrolysable sylane groups.
 6. Themultilayer composition according to claim 4, wherein (XPO) has a degreeof cross-linking of at least 40% by weight.
 7. The multilayercomposition according to claim 4, wherein (XPO) has a degree ofcross-linking of at most 95% by weight.
 8. The multilayer compositionaccording to claim 4, wherein (PM) is selected from the group consistingof polycarbonates, acrylic polymers, polyacrylates, cyclic polyolefins,metallocene-catalyzed polystyrene, polyethylene terephthalate (PET),polyethylene terephthalate bioriented (BOPET), polyethylene naphthalate,fluoropolymers, and laminates, mixtures or alloys of two or morethereof.
 9. The multilayer material according to claim 4, wherein layer(a) comprises or consists of glass.
 10. A process of the preparation ofthe multilayer composition according to claim 4, comprising the stepsof: i. providing the layer (a); ii. applying on at least a portion ofthe (a) layer of step i. a composition comprising the cross-linkablepolymer comprising hydrolysable silane groups (SPO), and optionallysuitable additives; iii. cross-linking (SPO) to obtain a multilayercomposition wherein the cross-linked polyolefin (XPO) adheres directlyto at least a portion of (a).
 11. An article comprising the multilayercomposition according to claim
 4. 12. The article according to claim 11in the form of a photovoltaic cell or of a safety glass.
 13. Thecross-linkable polyolefin of claim 2, wherein the weight ratio of(c1):(c2) in (CB) is from 80:20 to 20:80.
 14. A multilayer compositioncomprising: (a) at least one layer of glass, of a metal or of apolymeric material (PM), and (b) a least one polymeric layer comprisinga cross-linked polyolefin (XPO) obtainable by hydrolysis andcondensation of a cross-linkable polyolefin comprising hydrolysablesilane groups [cross-linkable polymer (SPO)] according to claim 2,wherein b) adheres directly to at least a portion of (a) and (PM) isdifferent from (XPO).
 15. A multilayer composition comprising: (a) atleast one layer of glass, of a metal or of a polymeric material (PM),and (b) a least one polymeric layer comprising a cross-linked polyolefin(XPO) obtainable by hydrolysis and condensation of a cross-linkablepolyolefin comprising hydrolysable silane groups [cross-linkable polymer(SPO)] according to claim 3, wherein b) adheres directly to at least aportion of (a) and (PM) is different from (XPO).
 16. The multilayercomposition according to claim 5, wherein (XPO) has a degree ofcross-linking of at least 40% by weight.
 17. The multilayer compositionaccording to claim 6, wherein (XPO) has a degree of cross-linking of atmost 95% by weight.
 18. The multilayer composition according to claim 5,wherein (PM) is selected from the group consisting of polycarbonates,acrylic polymers, polyacrylates, cyclic polyolefins,metallocene-catalyzed polystyrene, polyethylene terephthalate (PET),polyethylene terephthalate bioriented (BOPET), polyethylene naphthalate,fluoropolymers, and laminates, mixtures or alloys of two or morethereof.
 19. The multilayer composition according to claim 6, wherein(PM) is selected from the group consisting of polycarbonates, acrylicpolymers, polyacrylates, cyclic polyolefins, metallocene-catalyzedpolystyrene, polyethylene terephthalate (PET), polyethyleneterephthalate bioriented (BOPET), polyethylene naphthalate,fluoropolymers, and laminates, mixtures or alloys of two or morethereof.
 20. The multilayer composition according to claim 7, wherein(PM) is selected from the group consisting of polycarbonates, acrylicpolymers, polyacrylates, cyclic polyolefins, metallocene-catalyzedpolystyrene, polyethylene terephthalate (PET), polyethyleneterephthalate bioriented (BOPET), polyethylene naphthalate,fluoropolymers, and laminates, mixtures or alloys of two or morethereof.